Method and System for Document Authenticity Verification

ABSTRACT

The invention provides a system and method for secure document verification. In the preferred embodiment, embedded information consists of marks embedded in the interior of the document and are comprised of regions that have refractive index modified to carry information. In the preferred embodiment the marks are not discernable by conventional imaging, spectroscopic or optical polarization techniques, but are discernably by interferometric techniques, such as optical coherence tomography. Multiple alternate embodiments are taught.

CROSS REFERENCES TO RELATED PATENTS OR APPLICATIONS

This application claims priority from U.S. provisional patentapplication No. 62/197,079, filed Jul. 26, 2015, the entirety of whichis incorporated by reference as if fully set forth herein.

This invention is related to U.S. Pat. No. 7,526,329 titled Multiplereference non-invasive analysis system and U.S. Pat. No. 7,751,862titled Frequency resolved imaging system, the contents of both of whichare incorporated by reference herein as if fully set forth.

FIELD OF USE

The invention relates to non-invasive imaging and analysis techniquessuch as Optical Coherence Tomography (OCT). In particular it relatesusing optical interferometric techniques to monitor or measuresub-surface attributes of documents such as bank notes (paper currency),legal documents or documents containing highly confidential information.

BACKGROUND OF THE INVENTION

Non-invasive imaging and analysis of targets using optical coherencetomography (OCT) is a powerful technique for acquiring sub-surfaceinformation embedded in targets without damaging the target or systembeing analyzed.

The embedded information in a particular sheet of paper of base documentcan be imaged and analyzed by Optical coherence tomography (OCT), atechnology for non-invasive imaging and analysis. There are more thanone OCT techniques. Time Domain OCT (TD-OCT) typically uses a broadbandoptical source with a short coherence length, such as asuper-luminescent diode (SLD), to probe and analyze or image a target.

Multiple Reference OCT (MRO) is a version of TD-OCT that uses multiplereference signals. Another OCT technique is Fourier Domain OCT (FD-OCT).A version of Fourier Domain OCT, called Swept Source OCT (SS-OCT),typically uses a narrow band laser optical source whose frequency (orwavelength) is swept (or varied) over a broad wavelength range. InTD-OCT systems the bandwidth of the broadband optical source determinesthe depth resolution. In SS-OCT systems the wavelength range over whichthe optical source is swept determines the depth resolution.

Another version of Fourier Domain OCT, often referred to as SpectralDomain OCT (SD-OCT), typically uses a broad band optical source and aspectrometer to separate out wavelengths and detect signals at differentwavelengths by means of a multi-segment detector.

OCT depth scans can provide useful sub-surface information including,but not limited to: sub-surface images of regions of targets;measurement of thickness of layers of targets. More generally OCT depthscans can provide useful sub-surface information regarding attributes oftargets.

Documents, such as bank notes and legal documents require securityfeatures to protect against counterfeit documents. There is an on-goingneed for improved protection of valuable documents againstcounterfeiting. The ability of OCT to analyze information embeddedwithin a target enables adding a security layer to documents byembedding information or data during the manufacturing process of thepaper (or base document).

BRIEF SUMMARY OF THE INVENTION

The invention meets at least all of the unmet needs cited hereinabove.

The invention provides a system and method for secure documentverification.

In the preferred embodiment, embedded information consists of marksembedded in the interior of the document and are comprised of regionsthat have refractive index modified to carry information. In thepreferred embodiment the marks are not discernable by conventionalimaging, spectroscopic or optical polarization techniques, but arediscernable by interferometric techniques, such as optical coherencetomography. Multiple alternate embodiments are taught.

In the case of valuable or legal documents, such as bank notes,information can be systematically encoded in a manner that is difficultto reproduce, thereby providing additional barriers to counterfeiting.In the preferred embodiment the embedded information consists of marksembedded in the interior of the document and are comprised of regionsthat have refractive index modified to carry information. In thepreferred embodiment the marks are not discernable by conventionalimaging, spectroscopic or optical polarization techniques, but arediscernable by interferometric techniques, such as optical coherencetomography. In some embodiments the marks are systematically alignedspatially and constitute an encoded data sequence with error correctioncode-words. In some embodiments the marks are randomly spatiallydistributed in the manufacturing process of the paper of base document.

In the preferred embodiment, the method of uniquely identifying adocument of interest, comprises the steps of a) embedding in thedocument at least one region where said region has a predeterminedrefractive index; and b) scanning, using an optical coherence tomographydevice, said document and measuring optical path length data signalobtained from said embedded region.

The invention also teaches a method of manufacturing a secure documentbase material for wherein document authenticity is ensured by embeddedregions in said base material, where a first portion of said embeddedregions having at least a first refractive index and a second portion ofsaid embedded regions having at least a second refractive index, andwhere said first refractive index is not equal said second refractiveindex, such that said document authenticity is verifiable by measuringoptical path length using a scanning optical coherence tomographydevice.

Various alternate embodiments are taught, as can be seen by reference tothe figures included herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings provided as an aid to understanding the invention are:

FIG. 1 is an illustration of an edge-on or side view of a documentdepicting the location of the embedded data layer according to theinvention. It also depicts an en-face view of the document depictingtypical data mark and space sequences.

FIG. 2 depicts a short mark-space sequence; a detailed edge-on view ofthe mark-space sequence showing regions of different refractive index;and the associated data pattern.

FIG. 3 depicts the short mark-space sequence of FIG. 2; a detailededge-on view of the mark-space sequence showing an alternate embodimentof the regions of different refractive index; and the associated datapattern.

FIG. 4 illustrates the data layer in a document and also illustrates anen-face view of the document depicting randomly spatially distributeddata mark and space regions.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The preferred embodiment of FIG. 1 illustrates an edge-on or side view101 of a document depicting the location of the embedded data layer 103.It also depicts an en-face view 105 of the document depicting thespatial outline of typical data mark and space sequences. Mark 107 is anoutline of one mark of a repetitive mark-space sequence used forregistration. Below the registration mark-space sequence are two datacarrying mark-space sequences.

Data can be encoded on the mark-space sequences by conventional dataencoding techniques such as a run-length encoding technique as used, forexample, encoding data on a DVD optical disc. Data integrity can beenhanced by the inclusion of error correction code-words, such as one ortwo dimensional Reed-Solomon error correction code-words.

An example of a short mark is depicted as mark 109 while region 111depicts two different length marks separated by a short space andpreceded and followed by spaces. An expanded view of this mark-spacesequence is depicted in the dashed rectangle 113.

FIG. 2 again depicts an en-face view of the mark-space sequence 201 witha double arrow 203 indicating the location of the cross-sectional oredge-on view of the same region 205 of the document. The detailededge-on view 205 of the mark-space sequence shows a top region 207 ofpaper (or the material of the document, which material is also referredto as the base document).

The region 207 is the top layer of the paper and has a refractive indexμ_(p) while the data layer 209 has alternating regions of two differentrefractive indices μ_(A) and μ_(B) corresponding to spaces and marks.The bottom layer of the paper 211 typically has the same refractiveindex μ_(p) as the top layer 207, although, if useful it could be adifferent refractive index.

An OCT probe beam indicated by 213 that acquires depth scans of thepaper, where such depth scans are in the direction indicated by theblock arrow 213 and where the optical probe beam also scans the paper ina lateral direction indicated by the arrow 215.

The data layer 209 has alternating regions of two different refractiveindices μ_(A) and μ_(b) corresponding to spaces and marks, the opticalthickness of the regions corresponding to the marks and the spaces. Thiscauses the optical path-lengths of the alternating regions to bedifferent, which causes the apparent distance to the layer boundary 217to vary depending on whether a space or a mark region is above it.

Similarly the apparent distance to the bottom surface of the paper 219varies depending on whether a space or a mark region is above the bottomlayer 211. The resultant optical path-length related data signal,depicted as 221, can be readily extracted from the interference signalor signals from a scanning OCT system.

A practical example of such data encoded paper would be the three layers207, 209 and 211 all being paper, but with the center layer 209 havingholes where the spaces of the mark-space array are located. The layersare bonded together with a bonding material with a refractive indexdifferent from the paper, that the fills the spaces.

An alternate embodiment is depicted in FIG. 3 where the edge-on view 305depicts a top paper layer 307 as before, but with the data layerconsisting of regions 309 with alternating values of refractive index,indicated by A and B, with a complimentary layer 311 of alternatingvalues of refractive index, indicated by B and A. The bottom layer 313is as before.

In this embodiment the optical path-length to the boundary 315 varieswith the different refractive indices and can be scanned by an OCTsystem to generate the data signal 317 from processed interferencesignals. This embodiment has the advantage that the total opticalthickness of the paper is substantially the same at any point.

An alternate embodiment is illustrated in FIG. 4 where an edge-on view401 of paper depicts the data layer 403. An en-face view 405 depicts thelocations of regions of different refractive index(s), with randomlyvarying shape, that are distributed randomly through-out the paper (orbase document).

In one embodiment the regions of different refractive index consist ofadhesive or bonding material that has a refractive index different fromthe refractive index of the paper. The irregular shapes and randomdistribution are a consequence of the manufacturing and bonding processof the two components of the paper.

A detailed view of the cross-section of a region indicated by 407 isdepicted in 409 where the top portion 411 of the paper has voids, one ofwhich is indicated by 413, which are filled by the adhesive or bondingmaterial with refractive index μ_(A) different from the refractive indexμ_(p) of the paper. Also depicted is the bottom portion 415 of the paperwhich also has a refractive index μ_(p).

OCT depth scans of the paper are processed to generate a data pattern ata depth indicated by the dashed arrow 417. The voids, such as 413, thatare filled with the bonding material are either a natural consequence ofthe paper manufacturing process or embossed by a template with apseudo-random pattern.

In another embodiment a spatially aligned pattern of voids is imposed orembossed on one portion of the paper to generate a spatially aligneddata pattern based on voids filled with bonding material (and the spacesbetween them).

In another embodiment, the paper (or base document) consists of one ormore layers and the random data pattern is a consequence of randomlydistributed structural elements that are generated by the manufacturingprocess, and where such structural elements are discernable by an OCTsystem.

Aligned data patterns provide added security against counterfeiting oflegal documents, such as bank notes, by including an OCT scanner in banknote readers. In one embodiment where one or more data sequences arealigned with known locations on the document, the additional securityresides in the difficulty in reproducing the paper with these securitymarks included.

Such data sequences are very robust, availing of conventional channelcoding, such as (2, 10) run length limited coding and conventional errorcorrection techniques, such as Reed Solomon error correction code-words,similar to those of a DVD disc data sequence.

In another embodiment, OCT is used to scan the complete document andthereby acquire a complete volume image of the scattering properties ofthe document. Random structural elements provide the equivalent of a 3Dfingerprint of the document.

Using a manufacturing process that ensures such structural elements arerandomly distributed ensures each 3D fingerprint is unique and extremelydifficult to counterfeit. Here the additional security resides in thedifficulty in reproducing the document with the same 3D fingerprint.

Various security systems can be devised based on combinations of imposedaligned data mark sequences and one or more segments of the random 3Dfingerprint. This general approach is enabled by the ubiquitousavailability of a low cost OCT scanner.

For example a bank note including one or more data sequences,discernable only by an OCT reader are embedded in the structure of thepaper aligned with known locations on the bank note. The authenticity ofthe bank note is determinable by an OCT scanner that is installed in aconventional bank note analyzer where such an OCT scanner has access toinformation about the embedded data.

In some embodiments the information about the embedded data available tothe OCT scanner is the error corrected data. In other embodiments theinformation about the embedded data available to the OCT scanner is ahash of the error corrected data.

Additionally details of the location and 3D image of a small portion ofthe 3D fingerprint of the paper of the bank note is available to the OCTscanner.

In some embodiments the particular small portion of the 3D fingerprintof the paper of the bank note used in the above manner is periodicallychanged to a different location on the bank note.

Many variations of the above embodiments are possible. The embodimentsare applicable to documents other than bank notes, such as credit cards,driving licenses, passports, wills property titles, etc. The scope ofthis invention should be determined with reference to the descriptionand the drawings along with the full scope of equivalents as appliedthereto.

1. A method of uniquely identifying a document of interest, saiddocument of interest being composed of at least a first material,comprising the steps of: obtaining optical coherence tomography depthscans of said first material, said first material having a firstrefractive index and within said first material a second material havinga second refractive index, and where said second material occurs as aconsequence of manufacturing of said first material; processing saiddepth scans; generating a data pattern at a predetermined depth, wheresaid data pattern constitutes a unique identifier said document ofinterest.
 2. The method of claim 1 wherein said second material isintroduced as an adhesive material in the course of manufacture of saiddocument of interest.
 3. The method of claim 1 further including thestep of obtaining OCT depth scans of two or more layers in said firstmaterial.
 4. The method claim 1 further including the step of obtaining,using optical coherence tomography, a three dimensional image of a smallportion of said document of interest, which said image and location ofsaid image serve to uniquely identify said document of interest.
 5. Amethod of uniquely identifying a document of interest, said document ofinterest being composed of at least a first material, comprising thesteps of: obtaining optical coherence tomography depth scans of saidfirst material, said first material having a first refractive index andwithin said first material a second material having a second refractiveindex, and where said second material occurs as a predeterminedconsequence of manufacturing of said first material; processing saiddepth scans; generating a data pattern at a predetermined depth, wheresaid data pattern constitutes a unique identifier said document ofinterest.